1. Field of the Invention
The present invention relates to a driving device to be applied to a thin-disc-shaped stepping motor or actuator.
2. Description of the Related Art
Heretofore, a brushless motor can be cited as a model suitable for a small motor. Examples of a brushless motor of which the driving circuit is simple include a small cylindrical stepping motor which uses a permanent magnet, such as that shown in FIG. 16.
FIG. 16 is a cross-sectional view illustrating the internal configuration of a stepping motor according to a known example.
In FIG. 16, a stator coil 105 is wound around a bobbin 101 concentrically, and the bobbin 101 is sandwiched and fixed with two stator yokes 106 from the shaft direction. With the stator yoke 106, stator gear teeth 106a and 106b are alternately disposed in the circumferential direction of the inside diameter surface of the bobbin 101. A stator 102 is configured in a case 103 by the stator yoke 106 integrated with the stator gear tooth 106a or 106b being fixed.
Of the two cases 103, one case 103 is fixed with a flange 115 and a shaft bearing 108, and the other case 103 is fixed with another shaft bearing 108. A rotor 109 is made up of a rotor magnet 111 fixed to a rotor shaft 110. The rotor magnet 111 makes up an air gap portion in a radial pattern together with the stator yoke 106 of the stator 102. The rotor shaft 110 is supported between the two shaft bearings 108 so as to be rotated.
As for a modification of a stepping motor having the above configuration, an optical control device has been proposed (see Japanese Patent Publication No. 1978-2774, for example). An optical control device is for controlling the passage amount of light by opening/closing a shutter blade to be coupled with a stepping motor in stages. Also, as for another modification, a hollow motor has been proposed (see Japanese Patent Laid-Open No. 1982-166847, for example). A hollow motor is a stepping motor having a ring-shaped configuration, which allows light or the like to pass through the cavity of the center portion thereof.
Also, with the shutter or diaphragm adjustment mechanism of a camera or the shutter of a digital camera, or a camera which employs a silver halide film, upon attempting to subject a photographing lens to downsizing and reduction in shaft length, the photographing lens needs to be positioned before and after the shutter or diaphragm adjustment mechanism. Accordingly, thinning in the light path i.e. axial direction of the shutter or diaphragm adjustment mechanism is desired as well as high-outputting of a motor.
However, with the known small cylindrical stepping motor shown in FIG. 16, the case 103, bobbin 101, stator coil 105, and stator yoke 106 are disposed concentrically on the outer circumference of the rotor 109. Accordingly, this provides a disadvantage wherein the outer dimension of the stepping motor becomes large. Also, the magnetic flux generated by electric power being supplied to the stator coil 105 principally passes through the end surface 106a1 of the stator gear tooth 106a and the end surface 106b1 of the stator gear tooth 106b, as shown in FIG. 17. Accordingly, the magnetic flux does not act upon the rotor magnet 111 effectively, resulting in a disadvantage wherein the output power of the stepping motor is low.
Also, with the above optical control device described in Japanese Patent Publication No. 1978-2774, and the above hollow motor described in Japanese Patent Laid-Open No. 1982-166847, as with the above description, a stator coil and a stator yoke are disposed on the outer circumference of a rotor magnet. Accordingly, the outer dimension of the motor becomes great, and also the magnetic flux generated by electric power being supplied to the stator coil does not act upon the rotor magnet effectively.
In general, a camera employs a mechanism for driving a diaphragm blade, shutter, photographing lens, or the like using a motor. However, in the event that a type of motor such as shown in FIG. 16 is disposed so as to be parallel to the light axis within the lens barrel of a camera, and it is attempted to be used for driving a diaphragm blade, shutter, photographing lens, or the like, this type of motor has a solid cylindrical shape, the following problems may be encountered. The radial dimension of the lens barrel is a value obtained by adding the radial dimension of the motor to the radial dimension of the photographing lens or the radial dimension of the diaphragm opening portion, so it is difficult to suppress the diameter of the lens barrel to a sufficient small value. Also, with this type of motor, the dimension in the light axial direction is long, so it is difficult to dispose the photographing lens near the diaphragm blade or shutter blade.
On the other hand, a thin motor of which the dimension in the shaft direction is short such as shown in FIGS. 18 and 19 has been proposed (see Japanese Patent Laid-Open No. 1995-213041, and Japanese Patent Laid-Open No. 2000-50601, for example).
FIG. 18 is a perspective view illustrating the configuration of a known brushless motor, and FIG. 19 is a cross sectional view illustrating the internal configuration of the same brushless motor.
In FIGS. 18 and 19, the brushless motor comprises multiple coils 301, 302, and 303, a disc-shaped magnet 304, and so forth. The coils 301 through 303 have a thin coin shape, and the axis thereof is disposed in parallel with the axis of the magnet 304. The magnet 304 is magnetized in the shaft direction of the disc, and the magnetized surface and the axes of the coils 301 through 303 are disposed so as to face the magnet 304.
In this case, the magnetic flux to be generated from the coils 301 through 303, as shown in the arrow in FIG. 19, does not act completely effectively upon the magnet 304. Also, the rotational force which the magnet 304 generates acts at the center position of each of the coils 301 through 303, a distance L from the outer diameter of the motor. Accordingly, in spite of the size of the motor, the torque generated is small. Also, the coils 301 through 303 occupy up to near the center portion of the motor, so it is difficult to dispose another part within the motor.
Further, it is necessary to provide multiple coils 301 through 303, so this provides disadvantages such as complicating power supply control to the coils 301 through 303, and increases costs. Also, the coils 301 through 303 and the magnet 304 are disposed so as to be overlapped in the parallel direction as to the rotating shaft. Accordingly, in the event of employing this motor as a shutter or a diaphragm adjustment mechanism, the dimension in the light axial direction of the motor is long, so it is difficult to dispose the photographing lens near the diaphragm blade or shutter blade.
The present applicant has proposed a motor such as the following to solve such problems (see Japanese Patent Laid-Open No. 2003-219623 (U.S. Pat. No. 6,897,579), for example).
This motor comprises a magnet, first and second coils, and first through fourth magnetic-pole portions. The magnet is formed in a hollow disc shape, and is made up of a first flat surface orthogonal to a center virtual shaft, a second flat surface orthogonal to the virtual shaft, an outer circumferential surface, and an inner circumferential surface. Also, the magnet is retained so as to be rotated with the center thereof serving as a rotational center, and also at least a surface perpendicular to the rotational center virtual shaft is divided in the angular direction (circumferential direction) centered on the virtual shaft to be magnetized to a different polarity alternately. The first coil is disposed outside of the outer circumferential surface of the magnet, and the second coil is disposed inside of the inner circumferential surface of the magnet.
The first magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the first coil. The second magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the first coil. The third magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the second coil. The fourth magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the second coil. Let us say that this type of motor is referred to as a first past example for the sake of facilitating description.
With the above configuration, the length in the shaft direction of the stepping motor is determined by the thickness of the magnet, and the magnetic-pole portion facing the thickness direction of the magnet, so the dimension in the shaft direction of the stepping motor can be reduced to be very small. Also, the magnetic flux to be generated by the first coil traverses the magnet present between the first magnetic-pole portion and the second magnetic-pole portion, so acts effectively. The magnetic flux to be generated by the second coil traverses the magnet present between the third magnetic-pole portion and the fourth magnetic-pole portion, so acts effectively. Thus, a high-outputting motor can be provided.
Also, an actuator employing the same method as the motor described in the above Japanese Patent Laid-Open No. 2003-219623 (U.S. Pat. No. 6,897,579) has been proposed (see Japanese Patent Laid-Open No. 2004-45682 (U.S. Pat. No. 6,781,772), for example). This actuator comprises a magnet, a coil, and first and second magnetic-pole portions. The magnet is formed in a hollow disc shape, and is made up of a first flat surface orthogonal to a center virtual shaft, a second flat surface orthogonal to the virtual shaft, an outer circumferential surface, and an inner circumferential surface. Also, the magnet is retained so as to be rotated with the center thereof serving as a rotational center, and also at least a surface perpendicular to the rotational center virtual shaft is divided in the angular direction (circumferential direction) centered on the virtual shaft to be magnetized to a different polarity alternately. The coil is disposed outside of the outer circumferential surface of the magnet.
The first magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. The second magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. Let us say that this type of actuator is referred to as a second past example for the sake of facilitating description.
Also, the following configuration can be conceived wherein a coil is disposed on the inner circumferential side of a magnet as an actuator similar to the actuator described in the above Japanese Patent Laid-Open No. 2004-45682 (U.S. Pat. No. 6,781,772). This actuator comprises a magnet, a coil, and first and second magnetic-pole portions. The magnet is formed in a hollow disc shape, and is made up of a first flat surface orthogonal to a center virtual shaft, a second flat surface orthogonal to the virtual shaft, an outer circumferential surface, and an inner circumferential surface. Also, the magnet is retained so as to be rotated with the center thereof serving as a rotational center, and also at least a surface perpendicular to the rotational center virtual shaft is divided in the angular direction (circumferential direction) centered on the virtual shaft to be magnetized to a different polarity alternately.
The coil is disposed inside of the inner circumferential surface of the magnet. The first magnetic-pole portion faces one of the surfaces perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. The second magnetic-pole portion faces the other surface perpendicular to the virtual shaft of the rotational center of the magnet with a predetermined gap, and is magnetized by the coil. Let us say that this type of actuator is referred to as a third past example for the sake of facilitating description.
However, the motor of the above first past example (Japanese Patent Laid-Open No. 2003-219623 (U.S. Pat. No. 6,897,579)) is a rotating member serving as output means, i.e., the magnet faces the first through fourth magnetic-pole portions with a gap. Accordingly, the thickness in the shaft direction of the motor is the dimension of sum of at least the first magnetic-pole portion, the gap between the magnet and the first magnetic-pole portion, the magnet, the gap between the magnet and the second magnetic-pole portion, and the second magnetic-pole portion. Or else, this is the dimension of sum of the third magnetic-pole portion, the gap between the magnet and the third magnetic-pole portion, the magnet, the gap between the magnet and the fourth magnetic-pole portion, and the fourth magnetic-pole portion.
Also, the rotational output of the magnet needs to be extracted from between the first magnetic-pole portion and the third magnetic-pole portion, or between the second magnetic-pole portion and the fourth magnetic-pole portion using a pin or the like. Extracting the output as a rotational shaft, such as a normal motor, further needs a member such as a disc or the like engaged with the above pin, and this makes the thickness of the motor further great in some cases.
Also, the actuator of the above second past example (Japanese Patent Laid-Open No. 2004-45682 (U.S. Pat. No. 6,781,772)) is also a rotating member serving as output means, i.e., the magnet faces the first and second magnetic-pole portions with a gap. Accordingly, the thickness in the shaft direction of the motor is the dimension of sum of at least the first magnetic-pole portion, the gap between the magnet and the first magnetic-pole portion, the magnet, the gap between the magnet and the second magnetic-pole portion, and the second magnetic-pole portion.
Also, the actuator according to the above third past example is a rotating member serving as output means, i.e., the rotational output of the magnet needs to be extracted from between the teeth of the first magnetic-pole portion and the second magnetic-pole portion, or from the outer circumferential side of the magnet using a pin or the like. Accordingly, the position for extracting the rotational output is stipulated, and the degree of freedom in the case of employing an actuator are restricted in some cases. Also, the magnet is fit to a member such as the bobbin outside of the coil or the like, so friction therebetween is great, it is sometimes difficult to obtain stable performance.